Compares the effectiveness of Lovastatin, Simvastatin, Pravastatin and Colestipol in patients with well-defined genetic causes of hypercholesterolemia. Examines the effect of these drugs in patients with familial hypercholesterolemia in whom this is due to a reduced number of receptors which bind LDL cholesterol and compare the response to patients with a disorder called familial defective apoprotein B-100 in whom the protein part of LDL does not bind normally to receptors.